Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are placed in a feed chute of an ink loader and a feed mechanism in the ink loader delivers the solid ink to a heater assembly. Solid ink sticks are either gravity fed or urged by a spring through the feed chute toward a heater plate in the heater assembly. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to a print head for jetting onto a recording medium. U.S. Pat. No. 5,734,402 for a Solid Ink Feed System, issued Mar. 31, 1998 to Rousseau et al.; and U.S. Pat. No. 5,861,903 for an Ink Feed System, issued Jan. 19, 1999 to Crawford et al. describe exemplary systems for delivering solid ink sticks into a phase change ink printer.
One problem faced in solid ink technology is differentiation and identification of ink sticks to ensure the correct loading and compatibility of an ink stick with the imaging device in which it is used. The wrong color of ink stick in a feed channel, ink sticks intended for different solid ink printers, use of non-qualified ink, etc. may impact image quality or even damage the solid ink imaging device. In previously known phase change ink systems, differentiation and identification of ink sticks was accomplished by incorporating keying features into the exterior surface of an ink stick. These features acted to exclude inappropriately configured ink sticks from being inserted into a feed channel of the printer.
World markets with various pricing and color table preferences have created a situation where multiple ink types may exist in the market simultaneously with nearly identical size/shape ink and/or ink packaging. Thus, ink sticks may appear to be substantially the same but, in fact, may be intended for different phase change printing systems due to factors such as, for example, market pricing or color table. Due to the broad range of possible ink stick configurations, marketing strategies, pricing, etc., differentiating the inks sticks so only appropriate ink is accepted by a printer requires methods of identification that go beyond physical keying.
The nature of solid ink technology renders the addition of conventional labels or tagging mechanisms to an ink stick impractical. Tags and labels must be removed before the ink stick is melted. Otherwise the tag or label material would clog the liquid ink components. One method that has been implemented to aid in the identification of an ink stick by a printer control system is the incorporation of encoding features into the exterior surface of ink sticks that interact with sensors in the ink loader. Ink stick data may be encoded into these features by configuring the features to interact with one or more sensors in an ink loader to generate a signal or coded pattern of signals that corresponds to information specific to the ink stick. Due to the soft, waxy nature of an ink stick body, features formed into the exterior surface of the ink stick may be easily damaged and, consequently, encoded data may be lost. Therefore, encoding features were typically large to make them less susceptible to handling damage and to ensure accurate reading by the sensor system in the ink loader. Larger features limit the information content that may be incorporated into an ink stick. The use of smaller encoding features that allow more information to be embedded into an ink stick, however, increases the likelihood of information corruption and incorrect sensing or reading due to the vulnerability of the soft ink material.